Castor's new appellate lawyer filed a motion in March, saying that a police interview with Castor, which contributed to her conviction, never should have happened because investigators knew she had a lawyer at the time, and that, as a result, information obtained in the interview should not have been allowed in court. No date has been set to argue the motion in court.

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Castor, who is serving her 51 1/3-year-to-life sentence in a New York State prison, continues to deny any wrongdoing, insisting that she's innocent.

"I did not kill David Castor," she said in an exclusive interview with ABC News' David Muir last May. "And I did not try to kill my daughter, period. And I will never say that I did. Ever."

Stacey Castor's Trial Pits Mother vs. Daughter

Castor stood before a judge and jury in January 2009 in the Onondaga County courthouse in Syracuse, N.Y., where she was given the chance to plead her innocence. Jurors listened to the testimony of more than 50 witnesses and deliberated for three days.

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Black Widow: The Mystery Begins

She was accused of murdering her second husband, David Castor, by poisoning him with antifreeze in 2005, and attempting to poison her daughter, Ashley Wallace, with a toxic cocktail of crushed pills and vodka. She also was suspected of murdering her first husband, whose grave lies next to Castor's.

"I think she's diabolical," assistant district attorney Christine Garvey said. "What she has done over the course of seven years is just unimaginable."

Castor's defense attorney, Charles Keller, said, "It's a tragedy for everybody. No matter how it comes out ... it's a tragedy. ... There is no happy ending."

Keller spent almost two years digging up a trail of evidence that, he said, pointed to a different murderer: Stacey Castor's then 21-year-old daughter, Ashley.

Stacey Castor alleged in court that her daughter had murdered both David Castor and Michael Wallace. If Ashley had indeed been responsible for Wallace's death, it would have meant that she killed her biological father by poisoning him with antifreeze at the age of 11.

"It may be easier for people to decide that I did it because I'm the mother," Stacey Castor said. "But kids do things like that. All you have to do is turn on the news or read the paper. There are children that kill children and other people every single day. It happens."

Castor hasn't spoken to either of her daughters since she was arrested at the hospital after Ashley Wallace nearly died in September 2007.

"You know, the truth will come out," Castor said. "I know that the truth is going to come out of this. The evidence will show that I am innocent. And I will go home."

Growing Suspicions

Ashley Wallace maintains, along with investigators, that Castor not only killed David Castor, but also killed Michael Wallace, her first husband and Ashley Wallace's father.

Wallace believes her mother tried to frame her for the deaths of both men.

But Wallace was confused, saying she never had written a note, and she hadn't taken any pills.

"It's just bald-faced evil," District Attorney William Fitzpatrick said. "[Ashley] almost died. She probably came within a couple of doses of Lexapro of dying. No one that I've ever prosecuted was so coldblooded, so heartless as this woman [Castor] was -- and so unemotional about it."

Wallace told ABC News that her mother once was her best friend, but that they have not spoken since the day of Castor's arrest.

Mysterious Death of Stacey Castor's Two Husbands

In 2000, Castor's first husband, the man she called "the love of her life," seemingly passed away from a heart attack. Wallace left Castor behind with their two daughters, Ashley, now 22, and Bree Wallace, now 19.

What's more, forensic lab workers said the exact same chemical was found in David Castor's body.

Police concluded that Wallace also had died from antifreeze poisoning, and that both men had been murdered.

His eldest daughter, Ashley Wallace, was distraught.

"I started crying. I got upset," she recalled. "Why would they dig up daddy? Like, he was resting peacefully. I thought it was inhumane, and I didn't like it whatsoever."

Soon, Stacey Castor became the main suspect. Police wiretapped her telephone calls, and in a conversation with close friend Dani Colman, detectives heard Stacey Castor's worry and her denial of accusations.

"It scares the living [expletive] out of me because I didn't do this," Castor said in one of her phone conversations.

Stacey Castor Found Guilty

When the verdict was delivered Feb. 4, 2009, Stacey Castor was in disbelief. She was found guilty of second-degree murder and second-degree attempted murder.

"I think honestly that was the best day of my life," Ashley Wallace said. "Because I knew that people knew, I knew that they knew that I didn't do it."

"We weren't allowed to present a defense. There were things that were allowed in that shouldn't have been, things that should have been that weren't," she said.

After being asked repeatedly, Stacey Castor did not say what evidence or which witnesses would have altered the result of the trial.

Despite her denials, a judge sentenced Stacey Castor to more than 50 years in prison, the maximum sentence.

"In my 34 years in the criminal justice system, I've seen murderers of every variety and stripe, but I have to say, Mrs. Castor, you are in a class by yourself," Judge Joseph Fahey said at the sentencing. "What you did to David Castor can only be described as premeditated torture.

"Now, as bad and as evil as that is, what you tried to do to your daughter Ashley is simply something that I find I almost can't comprehend," he added. "I've seen a lot of defendants come through this court system, but I've never seen one who was prepared to sacrifice their child to shift the blame away from themselves."

At the sentencing, Ashley Wallace said, "I didn't get a chance to say goodbye, and this will be the last time I get a chance. As horrible as it makes me feel, this is goodbye, Mom. As hard as you tried, I survived; and I will survive because now I'm surrounded by people that love me."

Family Divided After Verdict

Ashley Wallace recently graduated from college with near-perfect grades. She and her sister are trying to move on with their lives, and say they have no intention of ever again contacting their mother, who is serving her sentence in prison.

Castor's mother, Judie Eaton, visits her every month in prison, and is still convinced of her daughter's innocence. Easton has no contact with her granddaughters.

Prosecutors in the nearby county where Castor's first husband, Michael Wallace, died are still considering charging Castor for his murder. Some members of Wallace's family are eager to see the case go forward, 10 years after Michael's death, but authorities are hesitant to proceed because it would force daughters Ashley and Bree to endure another long, public trial.